Helical barbed tape is widely employed to define an elongated antipersonnel barrier that may be mounted on the ground, at the base of a fence or at the top of a supporting structure. The typical helical barbed tape comprises an elongated helically formed central support from which spaced apart clusters of barbs extend. Each cluster of barbs typically comprises a total of four barbs, with a first pair of barbs extending from a root on one side of the central support and a second pair of barbs extending from a second root on the opposite side of the central support. Each barb is an elongated generally flat member having opposed converging edges which intersect at a very sharp point. The barbs on opposed sides of the central supporting portion may be offset relative to the central support. An early version of a helical barbed tape of this general type is shown in U.S. Pat. No. 3,463,455 which issued to Meckel. Helical barbed tapes of the general type shown in U.S. Pat. No. 3,463,455 have received very substantial commercial success in view of their exceptional performance as an antipersonnel barrier.
Several improvements to the original Meckel barbed tape configuration have been made in recent years. In particular, double coil barbed tape barriers have been developed comprising an outer coil defining a helix having a first pitch and an inner coil defining a helix having a second pitch. The inner coil has been suspended generally centrally within the outer coil by a plurality of multistrand twisted cables extending therebetween. The use of inner and outer coils defining different respective pitches creates a substantially enhanced antipersonnel barrier. In particular, an intruder attempting to move between adjacent loops of the outer coil is likely to be stopped by the inner coil.
Another attempt to improve the basic structure of Meckel's U.S. Pat. No. 3,463,455 is shown in U.S. Pat. No. 4,503,423 which issued to Joseph J. Mainiero et al on March 5, 1985. In particular, U.S. Pat. No. 4,503,423 shows a single coil structure wherein adjacent loops in the coil are welded to one another at a plurality of spaced apart locations about each loop. The weldment between adjacent turns on the helical barbed tape is intended to continuously maintain opposed major surfaces of adjacent turns of the coil in abutting face-to-face surface contact to prevent longitudinal, radial or pivotal movement of adjacent turns relative to one another at the attachment points. The rigid permanent weldment of adjacent coils at a plurality of such attachment points defines a barrier much like the old concertina barrier which is intended to prevent intruders from slipping between adjacent coils.
Many helical barbed tape products include a helically extending reinforcing wire about which the central helical support of the barbed tape is wrapped. An early version of a barbed tape product of this general type is shown in U.S. Pat. No. 2,908,484 which issued to Uhl on October 13, 1959. The typical barbed tape product of this general type is manufactured by first wrapping a longitudinally extending barbed tape around the reinforcing wire, and then forming the combined tape and reinforcing wire into a helical configuration.
Several other improvements to helical barbed tape antipersonnel barriers have recently been made. For example, U.S. Pat. No. 4,718,641 which issued to Michael R. Mainiero on January 12, 1988 and which is asigned to the assignee of the subject application is directed to a helical barbed tape with reinforced barbs. The reinforcements formed in the barbs, as shown in U.S. Pat. No. 4,718,641, substantially increase the strength of the barbs, and thereby enable the use of a thinner gauge metal with no negative effects on the performance of the barbed tape. U.S. Pat. No. 4,718,641 also shows that a reinforcing wire can be used in combination with the barbed tape with reinforced barbs. The reinforcing wire provides further support for the central supporting portion of the barbed tape, thereby further ensuring the specified performance of the product even with a thinner gauge metal material for the tape.
The intrusion prevention art further includes electronic detection devices. In particular, it has been considered desirable to combine the physical barriers provided by helical barbed tape with an electronic detection means such that an attempt to breach the physical barrier will be electronically detected. The typical breach that should be protected against should include attempts to pass between coils, to cut the helical barbed tape and/or to crush the barrier with wooden planks, vehicles or the like.
One attempt to combine electronic intrusion detection devices with a barbed tape is shown in the above referenced U.S. Pat. No. 4,503,423. In particular, U.S. Pat. No. 4,503,423 attempts to use the helical barbed tape as a wave guide. A microwave transmitter is disposed at one end of the elongated helical barbed tape shown in U.S. Pat. No. 4,503,423 and directs a signal generally centrally through the helix defined by the barbed tape. A receiver is disposed at the other end of the barbed tape to receive the microwave signals from the transmitter. Variations in the received microwave signal may be indicative of an intrusion attempt.
Another prior art attempt to combine intrusion detection into an antipersonnel barrier is shown in U.S. Pat. No. 4,680,573 which issued to Ciordinik et al on July 14, 1987. Ciordinik shows a single coil barbed tape similar to the above referenced Uhl structure. However, the reinforcing wire shown in the single coil of U.S. Pat. No. 4,680,573 includes an electrical or optical conductor. The signal carried by the electrical or optical conductor will be varied or broken if the barbed tape or barbed wire is cut or crushed. Although the apparatus shown in U.S. Pat. No. 4,680,573 may be effective for detecting certain types of breaches to the antipersonnel barrier, it will be ineffective for detecting any type of breach that does not cut or substantially crush the wire.
The prior art also includes the combination of a standard chain link or barbed wire fence in combination with a linear length of coaxial cable transducer extending along the length of the fence and capable of producing an alarm when an intrusion or compromise of the fence is attempted. This prior art teaching is shown, for example, in U.S. Pat. No. 3,763,482 which issued to Burney et al on October 2, 1973. The apparatus shown in U.S. Pat. No. 3,763,482 includes a coaxial cable with a dielectric filler comprising a radially polarized electret which develops and transmits a signal along the cable in response to deformations of the cable at any point along its length. In particular, the cable shown in U.S. Pat. No. 3,763,482 may be clamped to a chain link or barbed wire fence in a generally linear disposition to generate an electrical signal in response to an attempt by an intruder to climb or cut the fence.
Still another prior art system is marketed under the trademark "PERISTOP" by Bigotec AG of Aaron, Switzerland, and comprises a galvanized hollow steel wire containing an insulated copper conductor. The "PERISTOP" wire may be installed inside a conventional barbed tape concertina. The "PERISTOP" apparatus is similar to the above referenced U.S. Pat. No. 4,680,573 to Ciordinik et al in that it is responsive only to the destruction or cutting of the wire.
U.S. Pat. No. 4,818,972 is a continuation-in-part of the above referenced U.S. Pat. No. 4,718,641 and was filed by the inventors herein and is assigned to the assignee of the subject invention. U.S. Pat. No. 4,818,972 shows the helical barbed tape with reinforced barbs and further including a central vibration-sensitive reinforcing cable, such as an electret cable, a piezoelectric cable or a vibration-sensitive geophone transducer cable. A general discussion of vibration-sensitive electret coaxial cables, geophone transducer cables or piezo-electric transducer cables is provided in Intrusion Detection Systems Principles of Operation and Application by Robert L. Barnard which was published in 1981 by Butterworth Incorporated of Woburn, Massachusetts.
Despite the desirable features found in certain of the above reference helical barbed tape antipersonnel barriers and certain electronic detection systems, it is desired to provide significant advances in the combination of these two art areas. In particular, the prior art electronic intrusion detection systems generally did not perform adequately as an antipersonnel barrier, while most prior art helical barbed tapes did not provide adequate detection of attempts to breach the physical barrier. With the exception of the above referenced co-pending application Ser. No. 125,471, the prior art attempts to combine intrusion detection with helical barbed tape antipersonnel barriers have been responsive to cuts in the helical barbed tape and/or complete crushing of the helical barbed tape, but not to most other attempts to breach the physical barrier. Some other prior art attempts to marry these two technologies, such as the wave guide in the above referenced U.S. Pat. No. 4,503,423, have provided structures that would perform under laboratory conditions, but which were impractical when applied in the field.
In view of the above, it is an object of the subject invention to provide an effective antipersonnel barrier that is operative to detect attempts to breach the physical barrier.
Another object of the subject invention is to provide an antipersonnel barrier that is responsive to cuts and crushing of the wire as well as any significant movement within the barrier.
It is an additional object of the subject invention to provide an intrusion detection system wherein an intrusion detection wire is physically protected by an array of antipersonnel barriers.
Still another object of the subject invention is to provide an antipersonnel barrier and intrusion detection system wherein the intrusion detection portions of the system are supported relative to the system for preventing false alarms.
Yet another object of the subject invention is to provide an antipersonnel barrier and intrusion detection system wherein the sensitivity of the intrusion detection system is readily adjustable.
It is a further object of the subject invention to provide an antipersonnel barrier that is easily and inexpensively manufactured and installed.
Another object of the subject invention is to provide an intrusion detection system wherein electronic components are protected from environmental moisture.